Arterio-venous shunt graft

ABSTRACT

A graft, for example, an arterio-venous shunt graft, is provided, which in a first aspect of the subject invention, is formed with longitudinal ribs. With fibrotic tissue ingrowth between the ribs, a composite rib/tissue layer is formed about the graft. The ribs provide counteracting lateral force against the embedded tissue to seal punctures formed therethrough during hemodialysis procedures. To provide additional surface area for puncturing, the graft may be formed with a truncated cross-section. With a second aspect of the invention, the graft is mounted onto a strip to prevent kinking, twisting or bending during an implantation procedure.

FIELD OF THE INVENTION

[0001] This invention relates to implantable prostheses, and, moreparticularly, to arterio-venous (AV) shunt grafts for hemodialysisapplications.

BACKGROUND OF THE INVENTION

[0002] Patients suffering from renal failure who undergo hemodialysistreatment require their blood to be readily accessible for suchtreatment. To avoid repeated puncturing of blood vessels, a techniquehas been developed in the prior art, wherein a graft is implanted thatacts as a shunt between an artery and a vein, such graft being aptlyreferred to as an arterio-venous (AV) shunt graft. Typically, the AVgraft is of relatively long length to provide maximum length for needlepuncturing. Because of the relatively long length, the AV grafttypically has a longer length than the spacing between the relevantartery and vein, and, as such, is often bent into a U-shape. Forimplantation, two relatively shallow channels are subcutaneously“tunneled” into the necessary U-shaped pattern, with a tunneller orguidewire being used to draw the AV graft into proper position. The endsof the graft are sutured, or are otherwise connected to, the selectedartery and vein.

[0003] To limit the amount of blood diverted through the AV graft, andaway from artery, the AV graft may have a tapered end at its arterialconnection. In this manner, blood flow through the AV graft isrestricted, without sacrificing surface area for needle puncture sites.

[0004] Although conventional AV grafts may provide relief for thevasculature, sealing of puncture sites therein is of major concernbecause of blood loss, as well as concern for the overall structuralintegrity of the graft. One approach to this problem has been indelaying a minimum number of days, often as long as two weeks or more,after implantation before puncturing the AV graft. The minimum delayperiod allows fibrotic tissue to surround the graft. Thus, uponpuncturing, the body is naturally able to cause a clot and restrictblood loss.

[0005] A second and different approach has been the use of self-sealinggrafts, which typically rely on fibrous material or sealant material toseal over a puncture. Examples of this approach are found in U.S. Pat.No. 4,619,641 to Schanzer; U.S. Pat. No. 5,192,310 to Herweck et al.;and U.S. Pat. No. 5,700,287 to Myers et al. Because of the additionalself-sealing material applied to this set of grafts, these AV graftsoften have relatively large diameters.

[0006] Due to the repeated puncturing of AV grafts, AV grafts have alimited life, regardless of design. Whereupon the structural integrityand/or the sealing ability of the AV graft becomes excessivelycompromised, a new AV graft is implanted into the patient at a newlocation. Patients who require hemodialysis over extensive periods oftime may have multiple AV grafts implanted in them. As is readilyapparent, it is desired to provide an AV graft having an extended life,to minimize the need for additional AV graft implantations in a patient.

SUMMARY OF THE INVENTION

[0007] In a first aspect of the subject invention, an AV shunt graft isprovided having longitudinal ribs formed on at least a portion of anouter surface thereof. The ribs act to encourage fibrotic tissueingrowth, resulting in a composite tissue/rib layer being formed aboutthe AV graft. The ribs apply a counteracting lateral force against anydisplaced embedded fibrotic tissue disposed between the ribs (when thereis a puncturing of the tissue), thereby aiding in the sealing thereof.

[0008] In a preferred embodiment, the AV graft is also at leastpartially truncated, having a generally D-shaped cross-section with theribs being located on an arcuate portion thereof. Upon implantation, theAV graft is positioned so that the arcuate portion faces the skin of thepatient. Accordingly, maximum surface area is provided for needlepuncturing. In comparing the subject invention with a conventional AVgraft, the profile length of the arcuate portion of the subjectinvention is formed longer than half the circumference of a conventionalcircular graft, to provide increased area for needle puncturing, whilethe cross-sectional area of the subject invention is at least equivalentto that of the conventional device so that sufficient flow area ismaintained.

[0009] In a second aspect of the invention, the AV graft is mountedonto, preferably by sintering, a flat strip prior to implantation. Assuch, the AV graft may be permanently pre-formed into a desired shapefor implantation (typically a U-shape), without concern for kinking,twisting, or bending, which are problems commonly experienced withimplantation of prior art AV grafts. In addition, the mounted AV graftis implantable as an integral unit, which requires a single tunnel to beformed, rather than two tunnels, as with conventional devices.

[0010] As a variation of the second aspect of the invention, a secondstrip may be mounted onto the top of the AV graft, to provide additionalrigidity and to enhance self-sealing characteristics. A layer of sealantmaterial may be disposed adjacent to the first and/or second strip.

[0011] These and other features of the invention will be betterunderstood through a study of the following detailed description andaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a perspective view of an arterio-venous (AV) shunt graftformed in accordance with a first aspect of the subject invention;

[0013]FIG. 2 is a cross-sectional perspective view of a graft having atruncated cross-section;

[0014]FIG. 2A is a cross-sectional view of a profile of a graft having atruncated cross-section;

[0015]FIG. 3 is a cross-sectional perspective view depicting various ribcross-sectional shapes usable with the subject invention;

[0016]FIG. 4 is a cross-sectional view showing an arrangement ofoverlapping ribs;

[0017]FIG. 5 is a perspective view of a graft mounted onto a strip readyfor implantation;

[0018]FIG. 6 is a cross-sectional view taken along line 6-6 of FIG. 5;and,

[0019]FIG. 7 is a similar view to FIG. 6, wherein the graft is formedwith a truncated cross-section.

DETAILED DESCRIPTION OF THE INVENTION

[0020] With reference to FIGS. 1 and 2, in a first aspect of the subjectinvention, a graft is provided having longitudinal ribs extendingtherefrom. It is envisioned that the use of ribs is particularlywell-suited for arterio-venous (AV) shunt grafts (“AV grafts”), althoughit may be used with other types of grafts, including endovasculargrafts. To illustrate the subject invention, reference will be made toAV grafts, although the ribs may be formed on other types of grafts.

[0021] Referring to FIG. 1, an AV graft 10 is shown, having a main body12 with an arterial end 14, a venous end 16, and a lumen 18 extendingtherebetween. The main body 12 may have a tapered portion 20 inproximity to the arterial end 14, so as to reduce the cross-sectionalarea of the lumen 18 at the arterial end 14. As such, the amount ofblood flow that is divertable through the AV graft 10 is limited. Themain body 12 may be formed of any material known to those skilled in theart used to form vascular prostheses, such as a textile material (e.g.,polyethylene terephthalate (PET)), a polymeric material (e.g., expandedpolytetrafluoroethylene (ePTFE)), or a composite thereof.

[0022] A plurality of ribs 22 are formed to extend from the main body12. In a preferred embodiment, the ribs 22 are unitarily formed on asleeve 24, with the rib 22/sleeve 24 structure being separately extrudedfrom the main body 12. With this preferred arrangement, the main body 12may be formed separately in accordance with similar techniques formanufacturing conventional AV grafts. The sleeve 24 desirably has aninternal diameter or lumen opening which is larger than the externaldiameter or dimension of main body 12 so that the sleeve 24 may beslipped over the main body 12 during assembly (e.g., with the main body12 being mounted on a mandrel), and caused to shrink thereonto. In suchcases, the sleeve 24 may be joined or immovably fixed to the main body12 using a variety of techniques including adhesive bonding, solventbonding, hot melt bonding or sintering. Sintering is particularlydesirable. It is also desired to have the internal lumen of the sleeve24 be smooth.

[0023] When sintering the sleeve 24 to the main body 12, heat isemployed. Optionally, pressure may also be employed. It is desirablethat the materials used to form the respective components have asoftening or sintering temperature which permits their bonding withoutdamage to their structural integrity. In one particularly desirableaspect of the invention, the body 12 and the ribs 22/sleeve 24structures are made of the same material, such as ePTFE.

[0024] As an alternative, the main body 12 may be extruded with the ribs22. If so, the ribs 22 would extend the full longitudinal length of theAV graft 10, which may not be desired in all cases.

[0025] Each of the ribs 22 is preferably formed generally straight toextend longitudinally along at least a portion of the AV graft 10. It ispreferred that the ribs 22 be coextensive with a major portion of themain body 12, yet be spaced from the arterial and venous ends 14 and 16,to allow for proper suturing or attachment thereof to the nativevessels. In addition, the ribs 22 are circumferentially spaced-apartabout the AV graft 10, and, preferably, are evenly-spaced. Because ofthe circumferential spacing, channels 26 are defined between the ribs 22into which fibrotic tissue may grow. With tissue ingrowth, a compositerib 22/tissue layer may be formed about the AV graft 10. In addition, itis preferred that the ribs 22 be formed of a material havingbiocompatibility, such as PTFE (particularly ePTFE). The ribs 22 reactto a puncture of the AV graft 10 by applying a counteracting lateralforce against any displaced embedded fibrotic tissue to limit bloodloss, and aiding in sealing any such punctures.

[0026] To enhance fibrotic tissue ingrowth, with reference to FIG. 3,the ribs 22 may be formed with various cross-sectional shapes, such as,but not limited to, rib 22A having a triangular cross-section; rib 22Bhaving a trapezoidal cross-section; rib 22C having a dove-tailcross-section; rib 22D having a semi-circular cross-section; and, rib22E having a pointed cross-sectional shape. Although not shown, othershapes are possible, such as a rectangular cross-section. Alternatively,as shown in FIG. 4, the ribs 22 may be formed to overlap, such asoverlapping ribs 22F, wherein the ribs 22F overlap portions of adjacentchannels 26. The overlapping ribs 22F not only encourage tissueingrowth, but act as flap valves in overlying any punctured, embeddedfibrotic tissue. Furthermore, the surfaces of the ribs 22, as well asthe channels 26, may be textured and/or treated with aningrowth-enhancing agent. As an alternative, a sealant material may bedisposed in the channels 26 to enhance self-sealing characteristics ofthe AV graft 10. The channels 26 may be filled to varying levels of thesealant, which would also allow for varying degrees of tissue ingrowth.

[0027] In a preferred embodiment, the AV graft 10 is at least partiallyformed with a truncated cross-section, as shown in FIG. 2. The length ofthe truncated cross-sectional portion of the AV graft 10 is preferablycoextensive with the ribs 22. In a preferred embodiment, the main body12 includes integrally formed first and second walls 28, 30, with thefirst and second walls 28, 30 preferably having different profiles. Thefirst wall 28 is preferably formed with a flat profile, whereas thesecond wall 30 is formed with an arcuate profile, thereby giving the AVgraft 10 a generally D-shaped cross-section. It is further preferredthat the profile length of the second wall 30 be greater than theprofile length of the first wall 28 so that, referring to FIG. 2A,length L2 of the second wall 30 is greater than length L1 of the firstwall 28. Upon implanting the AV graft 10, the first wall 28 ispositioned to face the patient's skin. By increasing the profile lengthof the second wall 30, as compared to conventional circular graftdesigns, additional surface area is provided for puncturing. As shown inFIG. 2A, it is preferred that the second wall 30 be formed with roundedcorners 32 in proximity to the first wall 28.

[0028] Other truncated cross-sectional shapes than that shown in theFigures may be used. For example, the rounded corners 32 need not beused with a-truncated circle being defined having the first wall 28follow a chordal path across a circular shape defined by the second wall30. In addition, the second wall 30 may define an elliptical profile.Furthermore, the first wall 28 may be formed with an arcuate profile (infact, as a flat profile, the first wall 28 is a curve formed about aradius equal to infinity). In addition, the first and second walls 28,30 may be formed with the same profile to provide a symmetricalcross-section (e.g., an oval), or different profiles.

[0029] To achieve the truncated cross-section, it is preferred that theAV graft 10 be sintered into the desired shape on an appropriatelyformed mandrel. Specifically, the AV graft 10 is initially oversized andtelescoped over the mandrel for sintering. Alternatively, the AV graft10 may be extruded with the truncated cross-section.

[0030] In determining the dimensions of the truncated cross-section, itis desired to at least maintain the same general cross-sectional areaavailable in conventional grafts, thereby ensuring that sufficientflow-through-area of the AV graft 10 is provided.

[0031] As noted above with respect to the ribs 22, the truncatedcross-sectional shape may be used in conjunction with grafts other thanAV grafts.

[0032] In a second aspect of the subject invention, the AV graft 10 isfixedly mounted onto a strip 34 prior to implantation. The strip 34 ispreferably formed of a biocompatible polymeric material, such as ePTFE,with the AV graft 10 being sintered thereto. As shown in FIG. 5,advantageously, the AV graft 10 may be fixedly mounted in a desiredshape, and maintained in that shape throughout implantation. It isenvisioned that the AV graft 10 will typically be pre-formed in aU-shape.

[0033] The strip 34 is optionally formed with a weakened region 36(e.g., an array of perforations) which allows for an implantable portion38 of the strip 34 to be separated from a handling portion 40 of thestrip 34. The weakened region 36 is located in proximity to the AV graft10, but preferably does not underlie any portion of the AV graft 10 and,thus, does not affect any of the connection between the AV graft 10 andthe strip 34. With the AV graft 10 being mounted onto the strip 34 priorto implantation, kinking, twisting and bending of the AV graft 10 can beavoided during implantation. Furthermore, with the fixed positioning ofthe AV graft on the strip 34, only a single tunnel need besubcutaneously formed in a recipient. Once implanted, the handlingportion 40 of the strip is detached from the implantation portion 38 bycausing failure of the weakened region 36, for example, by trimmingalong the array of perforations. If no weakened region 36 is provided,the handling portion 40 is detached, e.g., by trimming, from theimplantation portion.

[0034] The implantation portion 38 is preferably formed with a shorterlength than the AV graft 10 so as not to be coextensive therewith.Accordingly, the arterial and venous ends 14 and 16 are left free toallow for easy access in suturing or attachment thereof. It should alsobe noted that the strip 34 need not include the handling portion 40.

[0035] As a further variation, the AV graft 10 can be mounted onto thestrip 34 using an adhesive. Furthermore, as shown in FIG. 6, aself-sealing layer 42 may optionally be disposed between the strip 34and the AV graft 10, which may be an elastomeric polymer material or atextile have sufficient elastomeric or stretching features. Theself-sealing layer 42 serves to react to any punctures formedtherethrough to reduce blood loss. As a further variation, a secondarystrip 44 may be disposed atop the AV graft 10 so as to “sandwich” the AVgraft 10 therebetween, as shown in dashed lines in FIG. 6. The secondarystrip 44 would add further rigidity to the assembly in facilitating easeof implantation and additional sealing characteristics againstpunctures. A self-sealing layer 42 may optionally be disposed betweenthe AV graft 10 and the secondary strip 44.

[0036] As a result of utilizing the second aspect of the subjectinvention, not only will the life of the AV graft 10 be significantlyincreased, but also, operating time will be reduced and the implantationprocedure simplified. Furthermore, the fixed mounting of the AV graft 10prior to implantation will allow for an optimal bend radius to bepre-selected for flow characteristics in avoiding thrombus formation. Itshould also be noted that the second aspect of the subject invention maybe used in connection with or separate from the first aspect of thesubject invention and/or may be used with grafts other than AV grafts,as well as other implantable tubular conduits. As shown in FIG. 7, wherethe AV graft 10 is formed with at least a partially truncatedcross-section (as described above with respect to the first aspect ofthe invention), it is preferred that the first wall 28, having a shorterprofile, be fixedly mounted to the strip 34, with the second wall 30being free. Upon implantation, the second wall 30 is desirably orientedtowards the patient's skin to be punctured and may be optionally formedwith the ribs 22 (as shown in dashed lines in FIG. 7).

[0037] Various changes and modifications can be made to the presentinvention. It is intended that all such changes and modifications comewithin the scope of the invention as set forth in the following claims.

What is claimed is:
 1. An arterio-venous shunt graft comprising: atubular body having an interior surface and an exterior surface, aplurality of ribs extending from said exterior surface.
 2. A graft as inclaim 1, wherein said ribs extend longitudinally.
 3. A graft as in claim1, wherein said ribs are each generally straight.
 4. A graft as in claim1, wherein said ribs are circumferentially spaced-apart.
 5. A graft asin claim 1, wherein said tubular body includes a tubular sleeve, saidribs being formed unitarily with, and extending from, said sleeve.
 6. Agraft as in claim 1, wherein said ribs have a trapezoidal cross-section.7. A graft as in claim 1, wherein said ribs have a triangularcross-section.
 8. A graft as in claim 1, wherein said ribs have asemi-circular cross-section.
 9. A graft as in claim 1, wherein said ribshave a dove-tail cross-section.
 10. A graft as in claim 1, wherein saidribs have a pointed cross-section.
 11. A graft as in claim 1, wherein afirst of said ribs is circumferentially spaced from a second of saidribs with a channel being defined therebetween, said first rib at leastpartially overlapping said channel.
 12. A graft as in claim 1, wherein asealant material is disposed adjacent to at least a portion of saidribs.
 13. A graft is in claim 1, wherein said ribs are not coextensivewith said body.
 14. A graft as in claim 1, wherein said tubular body isat least partially defined by first and second integral walls, saidfirst and second walls collectively defining a truncated cross-section.15. A graft as in claim 14, wherein said cross-section is generallyD-shaped.
 16. A graft as in claim 14, wherein said first wall has ashorter profile length than said second wall.
 17. A graft as in claim14, wherein said ribs are not coextensive with said truncatedcross-section portion of said body.
 18. A graft as in claim 1, whereinsaid ribs are formed of a biocompatible material.
 19. A graft as inclaim 18, wherein said material is a polymeric material.
 20. A graft asin claim 19, wherein said material is expanded polytetrafluoroethylene.21. A graft comprising: a tubular body being at least partially definedby first and second integral walls, said first wall having a firstprofile, said second wall having a second profile, said first wallhaving a shorter profile length than said second wall.
 22. A graft as inclaim 21, wherein said first and second walls collectively define atruncated cross-section.
 23. A graft as in claim 22, wherein saidcross-section is generally D-shaped.
 24. A graft as in claim 21, whereinsaid first wall is generally flat.
 25. A graft as in claim 21, whereinsaid first wall is arcuate.
 26. A graft as in claim 24, wherein saidsecond wall is arcuate.
 27. A graft comprising: a tubular body being atleast partially defined by first and second integral walls, said firstwall having a first profile, said second wall having a second profiledifferent from said first profile.
 28. A graft as in claim 27, whereinsaid first wall has a shorter profile length than said second wall. 29.A graft as in claim 27, wherein said first and second walls collectivelydefine a generally D-shaped cross-section.
 30. A graft as in claim 27,wherein said first profile is generally flat.
 31. A graft as in claim30, wherein said second profile is arcuate.
 32. A graft assemblycomprising: a graft having a tubular body; and, a strip, said graftbeing mounted on said strip.
 33. An assembly as in claim 32, whereinsaid strip has portions extending beyond said graft.
 34. An assembly asin claim 33, wherein a weakened region is formed on said strip betweensaid graft and said portions of said strip which extend beyond saidgraft.
 35. An assembly as in claim 32, wherein said graft partiallyextends beyond said strip.
 36. An assembly as in claim 32, wherein saidgraft is an arterio-venous shunt graft.
 37. An assembly as in claim 36,wherein said graft is mounted on said strip with a general U-shape. 38.An assembly as in claim 32, wherein said tubular body includes aninterior surface and an exterior surface, a plurality of ribs extendingfrom said exterior surface.
 39. An assembly as in claim 38, wherein saidtubular body is at least partially defined by first and second integralwalls, said first and second walls collectively defining a truncatedcross-section.
 40. An assembly as in claim 39, wherein said ribs are notcoextensive with said truncated cross-section portion of said body. 41.An assembly as in claim 39, wherein said first wall has a shorterprofile length than said second wall.
 42. An assembly as in claim 41,wherein said graft is mounted to said strip via said first wall.
 43. Anassembly as in claim 32, further comprising a second strip, said graftbeing mounted to said second strip.
 44. An assembly as in claim 32,further comprising a self-sealing layer at least partially disposed onsaid strip.
 45. An assembly as in claim 32, wherein said strip comprisesa polymeric material.
 46. A method of implanting an arterio-venous shuntgraft, said method comprising: mounting a graft on a strip; preparing asubcutaneous tunnel at a desired location in a patient; implanting saidgraft in said tunnel; and connecting said graft to blood vessels to forma shunt therebetween.
 47. A method as in claim 46, wherein said graft ismounted on said strip to have a U-shape.
 48. A method as in claim 46,wherein said graft includes a tubular body having an interior surfaceand an exterior surface, a plurality of ribs extending from saidexterior surface.
 49. A method as in claim 48, wherein said graft isimplanted with said ribs at least partially facing the skin of thepatient.
 50. A method as in claim 46, wherein said graft includes atubular body being at least partially defined by first and secondintegral walls, said first wall having a profile length shorter thansaid second wall, said graft being mounted to said strip via said firstwall.
 51. A method as in claim 50, wherein said graft is implanted withsaid second wall facing the skin of the patient.
 52. A method as inclaim 46, further comprising mounting a second strip on said graft. 53.A method of implanting an arterio-venous shunt graft, said methodcomprising implanting in a patient a graft having ribs formed thereon,said ribs at least partially facing the skin of the patient, andconnecting said graft to blood vessels to form a shunt therebetween. 54.A method of implanting an arterio-venous shunt graft, said methodcomprising implanting in a patient a graft, said graft including atubular body being at least partially defined by first and secondintegral walls, said first wall having a profile length shorter thansaid second wall, said graft being implanted with said second wallfacing the skin of the patient, and connecting said graft to bloodvessels to form a shunt therebetween.
 55. A method as in claim 54,wherein said first and second walls collectively defining a truncatedcross-section.
 56. A method as in claim 55, wherein said cross-sectionis generally D-shaped.